A nonlinear toy model for jet noise modelling and control

Date

2025-08-29

Author

Karban, Uğur
Martini, Eduardo
Jordan, Peter

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Modelling and controlling jet noise are a notoriously difficult tasks, particularly at subsonic levels, dueto the subtlety of noise-generating mechanisms. Developing reduced-order models to study thesemechanisms and possible mitigation strategies is a well-established practice.In this study, we focus on developing a toy model for jet flow which incorporates the jitter effect to predictnoise generation and, eventually, control it. There exist similar flow models based on Ginzburg-Landau, parabolised stability, resolvent analysis, etc. However, none of these models have aninherent nonlinearity similar to the jitter in real jets. To include this effect, our model uses a train of freevortex rings.We perform a direct numerical simulation of discrete vortex rings shed from the edge of the nozzle as alow-fidelity flow model, incorporated with Howe’s acoustic analogy to calculate the noise generated by thesevortex rings. The interaction between the vortex rings is calculated using the Biot-Savart law, leading to anonlinear and chaotic behaviour akin to the jitter observed in jets. The difference between laminar andturbulent jets is mimicked by introducing random modulations in vorticity strength at the nozzle edge. Thisrandom modulation affects the chaotic behaviour of the vortex rings and, thus, the generated noise. Thenonlinear nature of the model presents a realistically challenging problem for noise control. The acousticfield generated by this vortex train model is shown in Figure 1. The top plot shows the power spectral density(PSD) obtained at various directivity angles. At each angle, the spectrum peaks around 𝑆𝑡 = 0.1, with higherPSD levels at lower directivities. A directivity plot is shown at the bottom indicating a superdirectivity akinto that of a jet. In the final paper, we will use various control approaches on this toy model and evaluate theirefficiency, which will help develop noise control strategies for real jets.

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https://airdrive.eventsair.com/eventsairwesteuprod/production-abbey-public/0de25870aad441b6aaf8e7119e9eb66a
https://hdl.handle.net/11511/118092

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Department of Aerospace Engineering, Conference / Seminar